A touch panel including a pressure-sensitive sensor corrects an input value and then obtains a corrected value to compensate for the deterioration of a resistive film that occurs when the touch panel is repeatedly used (for example, see Japanese Unexamined Patent Application Publication No. H5-250086).
For example, as shown in FIG. 1, a four-wire touch panel 102 has two sides, each made of a resistive film. One of the sides 104, i.e., a first side, is provided with electrodes 106 at both ends thereof in the direction of an X-axis and the other side 108, i.e., a second side, is provided with electrodes 110 at both ends thereof in the direction of a Y-axis. When the surface of the touch panel 102 is pressed, the resistive films on both of the sides are caused to contact each other where the surface is being pressed, thereby allowing the point of contact to be detected.
Specifically, when the resistive films on both the sides 104 and 108 are pressed into contact with each other as described above, a predetermined voltage is applied between the electrodes 106 at the both ends of the first side 104 for a period while the resistive films are in the contact state so that a voltage between the electrodes 110 on the second side 108 can be detected. During a subsequent period, a predetermined voltage is applied between the electrodes 110 at the both ends on the second side 108 so that a voltage between both the electrodes 106 on the first side 104 can be detected. From these detected voltages, an X-Y coordinate can be determined.
However, the touch panel 102 may have resistive films that are susceptible to variations in resistance values. In addition, when using the touch panel 102 described above in a typical fashion, contact points being pressed tend to be unevenly distributed. Therefore, deterioration of the resistive film may occur due to the wear and tear associated with repeated contact with certain points on the touch panel 102 may occur. Hence, a position input value is corrected to compensate for the deterioration of a resistive film, as disclosed in Japanese Unexamined Patent Application Publication No. H5-250086.
However, complicated signal processing may be necessary for such a correction, thereby requiring a user to perform a calibration operation. Therefore, a user is generally unable to perform the calibration operation should an error occur in an input coordinate.
In contrast, for a five-wire or eight-wire coordinate input device, for example, a touch panel that automatically corrects an input coordinate has been proposed. In this case, however, the configuration of the device and the production process thereof may become complicated because of an increase in the number of wires. Further, in order to automatically correct the input coordinate, complex computations are required. Thus, the automatic correction of an input coordinate for a 5 or 8 wire input device is difficult to implement.
On the other hand, an input device, such as an electromagnetic induction sensor, does not require correction of an input value to compensate for deterioration (see, for example, Japanese Unexamined Patent Application Publication No. H5-298007).
As shown in FIG. 2, an electromagnetic sensor 202 includes a plurality of loop coils 204 being arranged in X and Y directions. When a position indicator approaches any of these loop coils, a resonant circuit 206 incorporated in the position indicator resonates to compute an X-Y coordinate based on a resonance signal and a position of the loop coil selected by selector circuits 208. A coordinate-calculating circuit 210 calculates the coordinate of the input based on signals received from the selector circuits 208. Consequently, an input value (coordinate) does not need correction. However, in order to use the electromagnetic induction system described above, a specific position indicator is typically required. Thus, an input to the sensor 202 may not be made at any time without the position indicator.
Accordingly, there is a need for an improved input device that combines the position sensing functions of the electromagnetic induction system with the function of the touch panel.